Seat having relatively adjustable sections

ABSTRACT

A seat assembly having a base and two complementary seat elements supported thereon for individual yieldingly resisted universal tilting movement to accommodate to different positions of a user&#39;&#39;s body. The seat elements have recesses or apertures offset rearwardly from the universal connections for receiving the ischial tuberosity bones of the user, and the back of the seat has a localized recess for partial reception of the lumbar portion of the user&#39;&#39;s backbone. A peripheral upturned flange may be provided on the base in a relation enabling use of the assembly as a portable unit, to be removably positioned on a chair or the like, with the shiftable seat elements then being held by the flange against interfering contact with the chair. At the forward edges of the two shiftable seat elements, the assembly may be constructed to provide a more cushioned or yielding support than at other locations.

United States Patent 1 Berg et al.

[ SEAT HAVING RELATIVELY ADJUSTABLE SECTIONS [76] Inventors: Joseph A. Berg, 18670 Ventura Blvd., Tarzana, Calif. 91356; Loren W. Eames, 4233 N. Rick Rd., El Monte, Calif. 91732 [22] Filed: Aug. 30, 1971 21 Appl. No.: 175,821

[52] US. Cl. 297/312, 297/458 [51] Int. Cl A47c l/034, B60n 1/02 [58] Field of Search 297/312, 458-460 [56] References Cited UNITED STATES PATENTS 2,482,996 9/1949 Wisby 297/312 3,503,649 3/1970 Johnson 297/458 3,057,660 10/1962 Schneider.. 297/312 2,799,323 7/1957 Berg 1 297/312 3,080,195 3/1963 Berg 297/312 3,177,036 4/1965 Halter 297/454 [451 July 31, 1973 Primary ExaminerCasmir A. Nunberg Attorney -william P. Green [5 7] ABSTRACT A seat assembly having a base and two complementary seat elements supported thereon for individual yieldingly resisted universal tilting movement to accommodate to different positions of a user's body. The seat elements have recesses or apertures offset rearwardly from the universal connections for receiving the ischial tuberosity bones of the user, and the back of the seat has a localized recess for partial reception of the lumbar portion of the users backbone. A peripheral upturned flange may be provided on the base in a relation enabling use of the assembly as a portable unit, to be removably positioned on a chair or the like, with the shiftable seat elements then being held by the flange against interfering contact with the chair. At the forward edges of the two shiftable seat elements, the assembly may be constructed to provide a more cushioned or yielding support than at other locations.

15 Claims, 10 Drawing Figures Pmmnw w 3.749.442 I SHEU 1 UP 2 ZLqa/ .ELqa 3 JOSEPH A B526 LOAeEIU ml. EAMES INVENTORS SEAT HAVING RELATIVELY ADJUSTABLE SECTIONS BACKGROUND OF THE INVENTION This invention relates to improved seat assemblies which are especially designed to support the weight of a person with greater comfort than in conventional chairs, and to do so in a manner attaining automatic accommodation of the seat surfaces to slight movements of the user, while in all positions spreading the support forces over as wide an area as possible in order to avoid the development of localized pressure points and irritation.

In two prior U.S. Pats. Nos. 2,799,323 and 3,080,195, one of the present inventors has disclosed a seat structure in which two complementary seat elements or halves are located in side-by-side relation and are mounted for individual slight adjusting movement in a manner accommodating automatically to changes in position of a users body. The two seat elements are supported above a base structure, and are connected to that base by two separate universal connections mounting the seat elements for slight universal tilting movement relative to the base. This universal movement is resisted by appropriate cushioning means, such as springs interposed between the base and seat elements, or a layer of rubber or other cushioning material positioned at that location.

SUMMARY OF THE INVENTION The present invention provides certain improvements in the above discussed type of seat having two such relatively moveable seat elements. In particular, one feature of the invention relates to the construction of the universally moveable seat elements to have recessed or apertured areas at predetermined localized regions so positioned relative to the universal connections as to partially receive the ischial tuberosity bones of the user when the seat is in use, while at the same time enabling effective support of the seat by the universal connections, and permitting tilting adjusting movement of the seat sections in accordance with changes in position of the user's body. For this purpose, the localized regions for receiving the tuberosity bones are desirably located rearwardly of the centers of the universal connections, and for best results are slightly closer together than are the centers of the two connections. In the preferred arrangement, the regions for receiving the tuberosity bones are formed as localized recesses extending downwardly beneath other adjacent portions of the upper surfaces of the. seat elements. Alternatively, however, the seat elements may have openings at the specified locations for enabling downward movement of the tuberosity'bones, with cushioning material desirably being provided at the locations of the openings, and with the seat elements being shaped in slightly recessed fashion about the openings.

Another feature of the invention involves the formation of the seat assembly to provide a more cushioned support for the legs of the user near the front of the seat than toward the back of the seat, to thereby prevent the exertion of excessive force against the thighs and thus avoid the retarded circulation common in other seating. This is preferably accomplished by so forming the seat elements as to be bendable downwardly at their forward edges, and by giving them less support at those locations. In another form of the invention, however,

the yielding support at the front of the seat may be attained by shortening the two shiftable seat elements and providing a layer of cushioning material which extends forwardly beyond those seat elements to support the users legs at forward locations.

Other features of the invention have to do with the manner in which the assembly may be formed for use as a portable unit, to be placed on any convenient chair, automobile seat, or the like, and improve the comfort thereof. To enable such use, the base of the device carries a flange or flanges projecting upwardly from an edge or edges of the base and at the outside of the two shiftable-seat elements, so that these flanges may contact the back or arms of a supporting chair in a relation holding the shiftable elements out of interfering contact therewith, and thus permitting the desired automatic universal adjusting movement of the seat elements.

The seat preferably has a back which is contoured to have a lower portion of concave curvature as viewed from its forward side, and a reversely or convexly curved portion thereabove, with a unique vertical recess being formed in the center of the convex portion at a location to partially receive the backbone of a person using the seat, to thereby avoid the irritation usually caused by exertion of forces against the seat back by the backbone.

BRIEF DESCRIPTION OF THE DRAWINGS The above and other features and objects of the invention will be better understood from the following detailed description of the typical embodiments illustrated in the accompanying drawings, in which:

FIG. 1 is a perspective view of a first form of portable seat assembly constructed in accordance with the invention;

FIG. 2 is a plan view of the FIG. 1 seat;

FIG. 3 is a transverse section taken on line 3-3 of FIG. 2;

FIG. 4 is a section taken on line 4-4 of FIG. 3;

FIG. 5 is a central vertical section taken on line 5-5 of FIG. 2;

FIG. 6 is a horizontal section taken on line 66 of FIG. I; g

FIG. 7 is a fragmentary transverse section taken on line 7-7 of FIG. 2;

FIG. 8 is a view similar to FIG. 3, but showing a variational arrangement in which an opening is provided at v the location of each of the tuberosity bones;

FIG. 9 is a perspective view of another variational fonn of the invention; and

FIG. 10 is a front to rear section taken on line 10-40 of FIG. 9.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to the form of the invention shown in FIGS. 1 to 7, and particularly to FIG. 1, there is shown at 10 a portable seat assembly constructed in accordance with the invention and which is adapted to be placed on any chair, automobile seat, or other supporting surface represented generally at 11. The invention will be described primarily as applied to portable seat assemblies of this type, though it will be apparent that many features of the invention are equally applicable to structures in which the unit is a permanent built-in portion of a chair or the like.

The assembly of FIG. 1 includes a base 12 to which two complementary seat halves or elements 13 and 14 are mounted for limited individual adjusting movement. The main horizontal bottom portion 12 of base 12 preferably takes the form of a flat or planar sheet of material which as seen in plan view (FIG. 2) may be essentially square and of a width w and a front to rear dimension d (and which may have a number of stiffening ribs as shown at 71). Along its opposite side edges, the base 12 has two upturned parallel front to rear peripheral flanges 15 and 16, which may be formed integrally with the bottom horizontal portion 12 of the base, as by molding base 12 and its flanges 15 and 16 from an appropriate substantially rigid or stiff resinous plastic material, for example acrylonitrile butadiene styrene (ABS). At its rear edge, the base 12 may carry an upstanding seat back 17, which may also be molded integrally with the remainder of the base and is essentially rigid and adapted to support the back of a user.

Each of the two seat sections or seat elements 13 and 14 may also be molded from an appropriate resinous plastic material, typically the same material employed in making the base. The two sections 13 and 14 may both be substantially rectangular in peripheral outline, as seen in FIG. 2, having two parallel closely spaced inner front to rear edges 18, two outer essentially parallel edges 19 and 20, two generally transverse and generally aligned rear edges 21 and 22 disposed transversely of the front to rear central vertical plane 23 of the seat, and two front edges 24 and 25, desirably aligned with one another and disposed transversely of plane 23. The side edges 19 and of elements 13 and 14 may be spaced inwardly a short distance from the inner surfaces of the front to rear side flanges 15 and 16, as indicated at 26 in FIG. 2, to avoid interference by these flanges with the later-to-be-discussed universal pivotal movement of elements 13 and 14. Similarly, at the back of the seat assembly, the lower portion of back 17 is spaced a short distance from the rear edges 21 and 22 of seat elements 13 and 14, as indicated at 27 in FIG. 2, to avoid interference at that location with the universal movement of elements 13 and 14. When the back 17 is placed against the back 11' of a chair or car seat, the back 17 holds elements 13 and 14 in spaced relation to the back 11 of the underlying chair or seat, to thereby avoid interference by that structure with the pivotal movement of elements 13 and 14. In thesame way, the side flanges l5 and 16 prevent engagement of the outer side edges of seat elements 13 and 14 with an upstanding arm or side portion of a chair or car seat in which the unit may be placed.

Each of the seat halves l3 and 14 is mounted separately to base 12 by an individual universal connection represented at 28. As seen in FIGS. 4 and 7, each of these universal connections includes two brackets 29 and 30 cemented or otherwise secured rigidly to the base 12 and one of the seat elements 13 and 14, with an intermediate universal connector 31 being secured pivotally to brackets 29 and 30 for relative pivotal movement about two mutually perpendicular horizontal axes 32 and 33, in the manner of a conventional trunnion type universal connection. As will be apparent, other conventional types of connections attaining an essentially universal mounting may be substituted for the connections 28. The two universal connections 28 are located symmetrically with respect to the front to rear center plane 23 of the seat, being spaced equal distances in opposite directions from that axis, and having their centers positioned at the locations designated 34 and 35 in FIG. 2. These two locations 34 and 35 are near the center of the lateral width of the two elements 13 and 14 respectively, and are preferably spaced apart a distance s between about 5 and 7 inches, optimally about 6 inches.' The universal joints support elements 13 and 14 very positively and effectively at the locations of these connections, while allowing universal tilting or pivotal movement of elements 13 and 14 about essentially the locations 34 and 35 relative to base 12 and relative to one another to adjust to changes in the positioning of a person using the seat.

The two halves 13 and 14 extend approximately parallel to base 12, and therefore approximately horizontally, but may be contoured slightly as seen in FIGS. 3 and 4. More particularly, the elements 13 and 14 may curve up slightly at 36 near their back edge, and then curve downwardly at 37 to form a neat rolled edge giving an attractive overall appearance, and may similarly (as seen in FIG. 3) curve up slightly at 37' near their outer edges and then curve downwardly at 38 to form rolled side edges.

At two locations rearwardly of the universal connection centers 34 and 35, sections 13 and 14 have two 10- calized shallow recesses 41 and 42 which are so positioned as to receive the ischial tuberosity bones of a person using the seat. These recesses 41 and 42 are po sitioned and shaped symmetrically with respect to the front to rear center plane 23 of the seat, being spaced equal distances from that center plane at opposite sides thereof, and preferably having the essentially oval or egg-shaped peripheral configuration illustrated in FIG. 1, to converge angularly toward one another and re duce slightly in width as they advance forwardly. These recesses should have their centers and deepest portions 43 and 44 spaced apart a distance t which is less than the spacing s between the locations 34 and 35,,and is for best results between about 3% and 5% inches, optimally about 4% inches. Also, the front to rear spacing a between a transverse plane containing the centers or deepest portions of recesses 41 and 42 and a transverse plane 45 containing the universal connection centers 34 and 35 is preferably between about 2 and 3% inches, optimally about 2% inches. At the deepest portions of recesses 41 and 42, the upper surfaces of elements 13 and 14 are recessed downwardly to a level beneath that of the major portion of the remainder of the upper surfaces of these elements, and preferably beneath substantially all of the remainder of those upper surfaces. With particular reference to certain specific regions of the seatelements, the recesses 41 and 42 should be lower than the portions of the seat element surfaces which are located directly above the universal connections, and lower than portions of the surfaces which extend entirely about the recesses (as along the phantom line 69 of FIG. 2).

The universal tilting movement of elements 13 and 14 is resisted by two cushions 46 and 47, which may be formed of foam rubber or other appropriate resilient cushioning material, and which at their undersides are supported on and engage base 12, and at their upper sides support and engage elements 13 and 14. Cushions 46 and 47 may be substantially rectangular as shown, and desirably have central openings 48 to extend about and avoid interference with universal connections 28.

These openings 48 may be substantially larger than the universal connections, with small apertures 49 being provided in elements 13 and 14 at the locations of the openings 48, to allow a cooling circulation of air beneath the under and upper sides of elements 13 and 14. Cushions 46 and 47 normally maintain elements 13 and 14 in a predetermined substantially horizontal position, substantially parallel to portion 12 of the base, and resist universal tilting movement of elements 13 and 14 in any direction from those normal positions.

As seen in FIG. 4, each of the cushions 46 and 47 may be shorter in a front to rear direction than is the corresponding seat element 13 or 14, to terminate at a location 50 which is spaced from the forward edge 24 or 25 of element 13 or 14. Rearwardly of the location 50, the elements 13 and 14 are stiff enough to be substantially rigid and avoid deformation in use, while forwardly of location 50 and between that location and edge 24, the material of elements 13 and 14 is thinned substantially, as shown, and as a result of this thinning and the absence of any engaged portion of cushion 46 or 47, the front edge portions of elements 13 and 14 forwardly of locations 50 are free to be bent slightly downwardly by the legs of a user, as to the broken line position of FIG. 4. This affords a more cushioned support at the front of the seat than rearwardly thereof, to thereby avoid the exertion of upward forces on the forward portions of a persons legs which might tend to cut off circulation or cause discomfort.

Referring now to the configuration of the seat back 17, this back is shaped to have the contour illustrated in FIG. 5 as the seat back extends upwardly above the level of portion 12' of the base and above the level of the upper surfaces of elements 13 and 14. More specifically, as the seat back extends upwardly, it first advances rearwardly at 51, but curves progressively and concavely (as viewed from the front) up to a location 53. At that location the back reverses its curvature, to curve progressively and convexly from the location 53 to an upper edge 55 of the seat back. This general S- shaped curvature is provided across substantially the entire lateral width of back 17, except at the location of a central vertically extending rearwardly recessed region 56, lying essentially in the plane of the previously mentioned front to rear center plane 23 (the plane of FIG. 5). This recess is preferably formed only in the upper convexly curved portion 54 of the back, desirably extending upwardly from about the location 53 to a location near upper edge 55. The deepest central portion 56' of the recess is straighter than the convex surfaces 54 at opposite sides of the recess, and desirably extends substantially directly vertical, to provide for reception in the recess of the lumbar portion of the user's backbone when the seat is in use. It is found that this portion of the backbone tends to move rearwardly in a sitting position, and is most comfortable when a vertical recess of the type illustrated at 56 is provided for its reception. At the same time, the convex portions of the seat back at opposite sides of recess 56 effectively engage and support the user's back at opposite sides of the backbone, and the concave lower portion of the seat back supports the user most effectively at that location. For best results, the change of curvature location 53 of FIG. 5, and the lower end of recess 56, are spaced between about 4 and 7 inches above the level of the major portion of upper surfaces 57 of seat elements 13 and 14 (optimally about 6 inches) and both the convex curvature and recess continue upwardly to a level between about 9 and 12 inches (optimally 10 inches) above the major portion of surfaces 57.

To now describe the manner of use of the arrangement of FIGS. 1 to 7, assume that the unit 10 has been placed on an appropriate chair or seat 1 l, with back 17 resting against the back 11' of the supporting seat. When a user then sits on the two seat elements or halves 13 and 14, his weight is normally supported by these units essentially as though the weight were centered at approximately the locations of universal joints 28, so that the cushions 46 and 47 can easily hold elements l3 and 14 in approximately their normal horizontal positions. The tuberosity bones of the user project downwardly into the two recesses 41 and 42 in a manner relieving the tuberosity regions of excessive forces, and thereby maximizing the comfort of the user. After a person has used the seat for a period of time, he will automatically tend to shift his weight slightly from one side to the other, and/or to shift his legs slightly, with resultant automatic slight universal tilting or pivotal movement of one or both of the sections 13 and 14 essentially about the locations 34' and 35. Because of this shifting movement of elements 13 and 14, the body is still supported very effectively, and the tuberosity bones still remain in recesses 41 and 42, in spite of repeated shifts in the users weight. The reception of the lumbar portion'of the backbone within the shallow vertical recess 56 at the center of back 17 adds to the comfort, by avoiding the exertion of localized forces against the backbone; and the slight deflectibility of the forward edges of elements 13 and 14, between the locations 50 and 24 of FIG. 5, avoids the development of localized pressures at those locations against the legs. All in all, these various factors enable a person to sit on the seat with comfort for a much longer period of time than is possible with conventional chairs and seats.

FIG. 8 is a view similar to FIG. 3, but showing a variational arrangement in which an opening 58 is provided in each of the seat halves or elements 13a or 14a, at the locations of the tuberosity bone receiving recesses 28 of the first form of the invention. About the periphery of each of the openings 58, the seat element 13a or 14a may be recessed slightly and essentiallyannularly as shown at 28a, so that the tuberosity bones may project downwardly a short distance through the apertures 58 without presenting any sharp edges which might cause discomfort about the apertures. Also the cushions 46a and 47a, corresponding to cushions 46 and 47 of the first form of the invention, desirably have portions extending across openings 58, to resiliently support the tuberosity bones and the user's weight at those locations.

FIGS. 9 and 10 show another form of the invention, in which base 12b, corresponding to base 12 of FIG. 1, is typically illustrated as having, in lieu of the seat back 17 of FIG. 5, only a short upturned back flange 17b, whose upper edge extends just slightly above the level of the two shiftable seat elements 13b and 14b. These two seat havles may be the same as elements 13 and 14 of FIGS. 1 to 7 except that they are shorter in a front to rear direction, terminating forwardly at transverse edges 24b which are spaced a substantial distance rearwardly of the front edge 59 of base 12b. Universal connections 28b may be identical with connections 28 of the first form of the invention, and the tuberosity bone receiving recesses 41b and 42b may be the same as recesses 41 and 42 in FIGS. 2 and 3.

Cushions 46b and 47b, formed of flat slabs or layers of foam rubber or the like, serve the purpose of cushions 46 and 47 of FIG. 2, but extend forwardly beyond the forward edges 24b of elements 13b and 14b, to provide front portions 60 which give yielding and very comfortable support to the forward portions of the legs of a user. An additional layer of cushioning material 61, typically of foam rubber or the like, may extend entirely across the upper side of the seat assembly, covering both of the elements 13b and 14b as well as the forwardly projecting portions of cushions 46b and 47b, and typically also extending downwardly at the sides and front of cushions 46b and 47b, as indicated at 62. An outer covering 63 of cloth or the like may extend across the upper side of this cushioning material and downwardly at the sides, front, and back of the seat, and then inwardly at the bottom of the seat to be retained there in appropriate manner and thereby provide a completely cushioned and completely upholstered seat having the advantages resulting from the relative universal pivotability of elements 13b and 14b, as well as the recesses 41b and 42b, and the softly cushioned forward portions forwardly of edges 24b. This assembly of FIGS. 9 and is especially well adapted for use as a permanently attached seat cushion in a chair, automobile seat, or the like, but as in the case of the other forms of the invention may also be employed as a portable type seat.

While certain specific embodiments of the present invention have been disclosed as typical, the invention is of course not limited to these particular forms, but rather is applicable broadly to all such variations as fall within the scope of the appended claims. We claim:

1. A seat comprising a base, two complementary seat elements positioned above the base, two universal connections mounting said seat elements for universal tilting movement relative to the base, and cushioning material interposed between said base and said seat elements and contacting said seat elements across part but not all of their horizontal extents and yieldingly resisting said universal tilting movement, said seat elements containing air circulation apertures providing communication between the upper side and underside of the seat elements at locations where the seat elements are not contacted by said cushioning material.

2. A seat as recited in claim 1, in which said cushioning material contacts each of the seat elements along a region extending essentially about but spaced from the corresponding universal connection, said apertures being formed in the seat elements at locations between said universal connections and the cushioning material extending thereabout.

3. A scat comprising a base structure, two complementary seat elements supported above the base structure in side-by-side relation; and two universal connections mounting said seat elements respectively for individual universal tilting movement relative to said base structure; said two seat elements having respectively two localized regions at locations to receive the ischial tuberosity bones of a user and constructed to allow projection of the users body downwardly farther at said regions than at other adjacent locations; said universal connections having their centers located forwardly of, and spaced farther apart than, the portions of said two localized regions at which the tuberosity bones can project downwardly the farthest.

4. A seat as recited in claim 3, in which said portions of said localized regions at which the tuberosity bones can project downwardly the farthest are spaced apart laterally between about 3% and 5 inches, and are spaced rearwardly of said centers of the universal connections between about 2 and 3% inches; and said centers of the universal connections are spaced apart laterally between about 5 and 7 inches.

5. A seat as recited in claim 3, including means between said base structure and both of said seat elements yieldingly resisting said universal tilting movement of the latter.

6. A seat as recited in claim 3, in which said localized regions form two recesses extending downwardly in the seat elements respectively and beneath other adjacent portions of the seat element about said regions.

7. A seat as recited in claim 3, in which said seat elements contain two openings at said localized regions for receiving the tuberosity bones.

8. A seat as recited in claim 7, in which said seat elements are slightly recessed downwardly about said openings.

9. A seat as recited in claim 8, including cushioning material between said base structure and said seat elements yieldingly resisting said universal tilting movement thereof and having portions at the locations of said openings.

10. A seat as recited in claim 7, including cushioning material between said base structure and said seat elements yieldingly resisting said universal tilting movement thereof and having portions at the locations of said openings.

11. A seat as recited in claim 3, including resilient cushioning material between said base structure and said elements yieldingly resisting said universal tilting movement of the elements, said seat elements having recesses extending downwardly at said localized regions beneath the level of adjacent portions of the seat elements which are disposed about said regions and portions located above said universal connections, said recesses in the two seat elements having their centers located between about 3%047150180 and 5% inches apart, said universal connections having their centers located between about 5 and -7 inches apart and being offset forwardly between about 2 and 3% inches from a vertical transverse plane containing the deepest portions of said recesses.

12. A portable seat assembly having a base adapted to be placed on and be supported by an underlying chair or seat structure, two complementary seat elements positioned above said base in side-by-side relation, two universal connections mounting said seat elements to the base for independent universal tilting movement, means between the base and said two seat elements yieldingly resisting said tilting movement, and a flange projecting upwardly from an edge of said base at a location beyond an edge of one of said seat elements in a relation to hold said edge of the seat element out of contact with an adjacent upwardly projecting portion of an underlying chair or seat structure.

13. A portable seat assembly as recited in claim 12, in which said flange extends forwardly along an outer side edge of one of said seat elements.

14. A portable seat assembly as recited in claim 12, across the back sides of both of said seat elements and in wl ich said flange extends across a back side of both extending forwardly along outer edges of both seat of said seat elements.

15. A portable seat assembly as recited in claim 12, mems in which said base carries a flange as recited extending 5 UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. 2 3,749,442

DATED 1 July 31, 1973 lN\/ ENTOR(S) I JOSEPH A5 BERG LOREN W EAMES It is certified that error appears m the above-Identified patent and that sald Letters Patent are hereby corrected as shown below:

The Patent is corrected to add a third inventor, Thomas W,

McAllister of Tarzana, California, in addition to the two originally listed inventors Joseph A0 Berg and Loren We Eamesa Signed and Sealed this Sixteenth D y f November 1976 [SEAL] Arrest.

RUTH c. MASON c. MARSHALL DANN Arresting Officer (ommissr'uner of Parents and Trademarks 

1. A seat comprising a base, two complementary seat elements positioned above the base, two universal connections mounting said seat elements for universal tilting movement relative to the base, and cushioning material interposed between said base and said seat elements and contacting said seat elements across part but not all of their horizontal extents and yieldingly resisting said universal tilting movement, said seat elements containing air circulation apertures providing communication between the upper side and underside of the seat elements at locations where the seat elements are not contacted by said cushioning material.
 2. A seat as recited in claim 1, in which said cushioning material contacts each of the seat elements along a region extending essentially about but spaced from the corresponding universal connection, said apertures being formed in the seat elements at locations between said universal connections and the cushioning material extending thereabout.
 3. A seat comprising a base structure, two complementary seat elements supported above the base structure in side-by-side relation; and two universal connections mounting said seat elements respectively for individual universal tilting movement relative to said base structure; said two seat elements having respectively two localized regions at locations to receive the ischial tuberosity bones of a user and constructed to allow projection of the user''s body downwardly farther at said regions than at other adjacent locations; said universal connections having their centers located forwardly of, and spaced farther apart than, the portions of said two localized regions at which the tuberosity bones can project downwardly the farthest.
 4. A seat as recited in claim 3, in which said portions of said localized regions at which the tuberosity bones can project downwardly the farthest are spaced apart laterally between about 3 1/2 and 5 1/2 inches, and are spaced rearwardly of said centers of the universal connections between about 2 and 3 1/2 inches; and said centers of the universal connections are spaced apart laterally between about 5 and 7 inches.
 5. A seat as recited in claim 3, including means between said base structure and both of said seat elements yieldingly resisting said universal tilting movement of the latter.
 6. A seat as recited in claim 3, in which said localized regions form two recesses extending downwardly in the seat elements respectively and beneath other adjacent portions of the seat element about said regions.
 7. A seat as recited in claim 3, in which said seat elements contain two openings at said localized regions for receiving the tuberosity bones.
 8. A seat as recited in claim 7, in which said seat elements are slightly recessed downwardly about said openings.
 9. A seat as recited in claim 8, including cushioning material between said base structure and said seat elements yieldingly resisting said universal tilting movement thereof and having portions at the locations of said openings.
 10. A seat as recited in claim 7, including cushioning material between said base structure and said seat elements yieldingly resisting said universal tilting movement thereof and having portions at the locations of said openings.
 11. A seat as recited in claim 3, including resilient cushioning material between said base structure and said elements yieldingly resisting said universal tilting movement of the elements, said seat elements having recesses extending downwardly at said localized regions beneath the level of adjacent portions of the seat elements which are disposed about said regions and portions located above said universal connections, said recesses in the two seat elements having their centers located between about 3 1/2 047150180 and 5 1/2 inches apart, said universal connections having their centers located between about 5 and 7 inches apart and being offset forwardly between about 2 and 3 1/2 inches from a vertical transverse plane containing the deepest portions of said recesses.
 12. A portable seat assembly having a base adapted to be placed on and be supported by an underlying chair or seat structure, two complementary seat elements positioned above said base in side-by-side relation, two universal connections mounting said seat elements to the base for independent universal tilting movement, means between the base and said two seat elements yieldingly resisting said tilting movement, and a flange projecting upwardly from an edge of said base at a location beyond an edge of one of said seat elements in a relation to hold said edge of the seat element out of contact with an adjacent upwardly projecting portion of an underlying chair or seat structure.
 13. A portable seat assembly as recited in claim 12, in which said flange extends forwardly along an outer side edge of one of said seat elements.
 14. A portable seat assembly as recited in claim 12, in which said flange extends across a back side of both of said seat elements.
 15. A portable seat assembly as recited in claim 12, in which said base carries a flange as recited extending across the back sides of both of said seat elements and extending forwardly along outer edges of both seat elements. 